GENERAL AND PLANNING INFORMATION

Transcription

1 BEETLE CONTENTS: Section 1: General and Planning information Section 2: Components and Material required Section 3: Assembly of the BEETLE Section 4: Wiring up the BEETLE Section 5: Electrical Testing DESCRIPTION BEETLE is a six-legged user programmable device. When it hits an object, BEETLE backs away, turns around and continues in another direction, imitating the actions of a real beetle. BEETLE also changes direction when it doesn't bump into anything for some time. BEETLE has a lever arm micro-switch at either end to detect an obstruction. It is driven by two motors, each with its own gearbox, and is controlled by a PICAXE-08M2 microcontroller. SECTION 1: 1. DESIGN CONSIDERATIONS 1.1 GENERAL 1 Section 6: Programming the Picaxe Section 7: Functional Test Section 8: Further Development Section 9: Theory GENERAL AND PLANNING INFORMATION BEETLE consists of a platform to which the components are attached. Legs and a link lever are located on each side of the platform. Before starting construction, plan, lay out and draw the components. Look at the BEETLE as a complete unit, and not just as separate parts. Our drawings can be used as a starting point for your design. 1.2 ITEMS FOR INVESTIGATION This project provides a number of different aspects of the BEETLE for investigation. Some ideas are listed below, in "Further Development" (at the end of this unit), as well as in the Theory section. The BEETLE you design can be evaluated for individuality, walking speed and smoothness, component layout and space efficiency. Create your own unique BEETLE design based on our drawings, which focus on component relationships, rather than dimensions. This provides scope for individual variation. Evaluate the suitability of various materials. For example: Aluminium, Perspex and PVC. SCORPIO TECHNOLOGY VICTORIA PTY. LTD. A.B.N Inverell Ave., Mt. Waverley, Vic Tel: (03) Fax: (03) Revised: 18 February sales@scorpiotechnology.com.au

2 Investigate adding more "intelligence" or different sequences to the program. Investigate other devices that could use two bi-directional motors and one switch input, such as the DIZZY. SECTION 2: COMPONENTS & MATERIAL REQUIRED 2.1 COMPONENTS SUPPLIED The following components are supplied in the kit: 2.2 ADDITIONAL REQUIREMENTS The following items are required and are available from Scorpio Technology: Battery AA, 4 required (BATTAA) AXE027 - PICAXE USB Download Cable, which can be ordered from us. The "AXE027 USB Cable Driver" can be downloaded for free from The following material is to be supplied by the student / designer: Electric hook-up wire Multi-strand in assorted colours Material for the components (PVC or acrylic sheet, plywood, etc.) NOTE: Plastic materials can be purchased from plastics suppliers (in the Yellow Pages under the heading Plastics Fabricators or search the Internet.) The PICAXE editor, which can be downloaded for free from The PICAXE programming editor software requires a PC running Windows XP or later. 2.3 TOOLS REQUIRED The following tools are required: Assorted hand tools Soldering equipment and solder Drill Bit 2.3mm (DB2.3) Drill Bit 2.6mm (DB2.6) Drill Bit 3.5mm (DB3.5) SECTION 3: 3.1 DESIGN ASSEMBLY OF THE BEETLE Determine dimensions for the platform, side pieces, legs and leg links. Determine a method of attaching the vertical side pieces to the platform (we used PVC adhesive, with small offcuts added to reinforce the joints - not shown in the drawings). 2

3 Position both gearboxes with their driving shafts in line with the centre of the platform, and a suitable distance apart (what happens if they re not in the centre?). Define the axle shaft length. Determine positions and attaching methods for: the PCB assembly (we glued spacers to the platform and used self-tapping screws to attach the PCB); the on/off switch; the micro-switches and the battery holder (preferably near the centre of gravity). HINT: Investigate alternate attachment methods, such as: hotmelt glue, screws, double-sided tape and hook-and-loop tape ("Velcro" or equivalent). Design Concept Determine a suitable operating speed. The MULTI-RATIO GEARBOX kit provides a choice of 3 gear ratios. Before starting, the desired gearbox ratio (which affects the device s speed) must be chosen, as this defines the parts to be used, and the assembly procedure (as detailed in Section 5: Assembling the Gearbox). NOTE: For details on gear ratios etc, refer to the section on Assembling the Gearbox. NOTE: For our BEETLE we used the TRIPLE-reduction version of the gearbox. 3.2 DIMENSIONAL RELATIONSHIPS Use our drawings as a guide only. Consider designing more "insect-like" body shapes and leg profiles. NOTE: these drawings are designed to show the relationships between the various dimensions, rather than defining the sizes that the BEETLE should be. 3

4 Dimensional Relations 3.3 ASSEMBLING THE PRINTED CIRCUIT BOARD ASSEMBLY PCB COMPONENT TERMINOLOGY Solder the resistors to the PCB. Trim the resistor leads and solder three of these to the PCB as wire links. The wire links are shown as straight lines on the PCB overlay. Solder the remaining components to the PCB in this order: IC sockets, three-pin header strip, stereo socket, LED, capacitors and electrolytic capacitor. Trim the component leads as required. CAUTION: Take care in the orientation of IC sockets, LED and electrolytic capacitor. Unsoldering and replacing damaged or wrongly positioned components will waste time. During soldering, do not overheat the PCB and components. WARNING: The electrolytic capacitor will be damaged and may cause injury if it is installed in the wrong direction and power is applied. PRINTED CIRCUIT BOARD WIRING DIAGRAM Do not insert the ICs into their sockets yet. These will be inserted just prior to testing. NOTE: For wiring, use different coloured wires to assist in tracing wires during fault finding. When soldering wires, strip a short piece of insulation from the end of the wire, twist the strands and "tin" them with solder. 4

5 3.4 ASSEMBLING THE GEARBOX GENERAL NOTES: the white gears, with the 1.9mm holes, are press fit onto the motor. the white gears, with the 2.4mm holes are press fit on to the gearbox shafts. The yellow spur gears free wheel on the gearbox shaft and have a 2.6mm diameter hole. MULTI-RATIO GEARBOX Assembly The 12T pinions are used as locators. Solder a 0.1uF capacitor across each motor s terminals. Assemble both gearboxes the same way. The choice of ratios available at the Gearbox Output shaft are: GEARBOX STAGE / Reduction ratio OUTPUT SHAFT RATIO Single reduction Hole A 1:5 Double reduction Hole B 1:25 Triple reduction Hole A 1:125 The motor, under load, turns at approximately these speeds. with 3 Volts (2xAA batteries) 6,500 RPM with 6 Volts (4xAA batteries) 12,600 RPM 3.5 ASSEMBLING THE GEARBOX HINT: Before starting assembly, cut (and de-burr) the steel rod to the designed length. Assemble the steel rod, and all the gears, to the gearcase - as shown in the appropriate drawing. The gears can be assembled onto the shaft/s with a help of small hammer. Press the 10T pinion onto the motor shaft. Hint: Place the gear on the bench, insert the motor shaft into the worm gear s hole and gently tap the end of the shaft (where it exits the motor) with a small hammer. Stop when the worm gear is 3mm from the motor s body. WARNING: Don t just push the motor down by hand as this can push the motor armature out of its bearings and jam the motor. Secure the motor to the gearbox case using the two self-tapping screws. Solder suitable lengths of wire to the motor terminals. 5

6 SINGLE REDUCTION (Low ratio = high speed) DOUBLE REDUCTION TRIPLE REDUCTION (High ratio = low speed) 3.6 ASSEMBLING THE BEETLE ASSEMBLY NOTE: Use a 2.3mm drill bit for pilot holes for self-tapping screw threads and for holes that have a press fit for the 2.5mm steel rod. The 2.6mm drill bit is used for drilling clearance holes for the gearbox shafts, and the 3.5mm drill for M3 screws, which attach the micro-switches. Attach the legs and link levers to the side plates. Use M3 Bolts, washers and "Nyloc" nuts (the Nyloc nut is a locking nut, and does not need to be done up tightly). Ensure that all components move freely. Fit the crank to each gearbox. Attach the crank to the corresponding link lever and leg. Position the gearbox assemblies on the platform. Drill holes for self-tapping screws in the platform to match the position of 2 diagonal holes in each gearbox case. Attach both motor and gearbox assemblies to the platform. Mount the PCB assembly to the platform. Form the lever arms of the micro-switches so that they form a gentle curve. Attach the micro-switches to the platform (using bolts and nuts). Attach the battery holder to the platform. SECTION 4: WIRING UP THE BEETLE NOTE: Refer to the PCB wiring diagram for more details. Solder the motor wires to the "Motor 1" and "Motor 2" connections on the PCB. Solder a length of wire between the "Normally Closed" terminals (usually marked with "NC" or "2") on both micro-switches. Solder a length of wire between the "Common" terminal (usually marked with a "C" or a "1") on one micro-switch to "SW2" on the PCB. Solder a length of wire between the "Common" terminal on the other microswitch to "SW3" on the PCB. Solder wires from the battery holder to the power switch. The red wire is positive and the black wire is negative. Solder a length of wire between the switch and the negative power connection (0V) and another length of wire to the positive power connection (V+). 6

7 Attach the on/off switch to the platform. SECTION 5: ELECTRICAL TESTING Inspect soldering for short circuits and poor "wetting" of component leads or pads. Insert four 1.5 Volt AA batteries into the battery holder. Move the power switch to "on". Check that the LED illuminates (this shows that power is available). If the LED does not illuminate: Check that the batteries are properly inserted in the battery holder. Check that the battery voltage is above 5.5 volts. (If low, replace the batteries.) Check that battery voltage is present between legs 1 and 8 on IC1. Leg 1 should be positive. Check the wiring against the wiring diagram. Check the values of the resistors against the circuit diagram. Check that the LED is the right way around. Check that the LED is working by using a 220 Ohm resistor and 6Volt (battery) power. Move the power switch to "off". Check the orientation of the ICs - the end with leg 1 is identified with a notch or dimple at one end. Line up the legs of each IC with its IC socket holes and press down firmly. Do not use the letters/numbers on the IC to identify leg numbers. NOTE: It may be necessary to bend the IC legs slightly to line them up with the socket holes. CAUTION: ICs will be damaged if they are installed in the wrong direction or if power supply (battery) connections are reversed. Position the jumper on the header strip so that it is in the "run" position. Move the power switch to "on". Check that the LED illuminates (this checks that power is available). If the PICAXE is not programmed, the motors will not turn and will not respond when the micro-switches are pressed. NOTE: At this stage nothing will appear to be working. SECTION 6: PROGRAMMING THE PICAXE 6.1 INSTALL PICAXE EDITOR NOTE: PICAXE editor needs to be installed once. Start up and log into your PC. (Some PCs require that you log in as the Administrator to install software. See your systems administrator if you do not have administrative rights.) From the website select "Free Software" > "Picaxe Programming Editor" > "Prog. Editor Installer". The installer will be downloaded to your computer. Select "Free Software" > "AXE027 USB Cable Driver". Download "Driver Installation Instructions". Download "Windows USB Driver (self extracting preinstaller format)". Install the PICAXE editor. 7

8 Install the AXE027 USB Download Cable driver. Follow the installation instructions. Insert the AXE-027 USB Download Cable into an available USB port. IMPORTANT: Always connect the AXE-2027 USB Download Cable to the same USB port. 6.2 START PICAXE EDITOR Click Start>Programs>Revolution Education>Programming Editor to start the software. If the Options screen does not automatically appear, click the View>Options menu. On the 'Mode' tab select PICAXE-08M2 mode. (The PICAXE-08M, with "12F683" written on it, is also compatible with BEETLE, but instead use the PICAXE-08M mode.) On the 'Serial Port' tab select the serial COM port allocated to the "AXE-027 PICAXE USB". Select Help>About. Check that the software version is or later. The PICAXE programming editor software is ready to use. 6.3 EDIT PROGRAM Copy our program into the PICAXE programming editor software. The program and flowchart are included in this document. Save the program. You can keep the original file. For changes use different file names. PROGRAM FLOW CHART 8

9 6.4 TRANSFER PROGRAM TO PICAXE Move the power switch to "off". Position the jumper to the "program" position. Connect the AXE-027 USB Download Cable between your PC and the stereo socket on the PCB. Move the power switch to "on". CONNECTING DOWNLOAD CABLE Run the PICAXE Programming Editor software and transfer our program to the PCB. When the program has finished downloading, one (or both) of the motors will begin to turn. If the Programming Editor software gives an error message stating that program cannot be transferred to the PICAXE: Carry out the checks listed in Section 5, Electrical Testing. Check that the cable is fully inserted into the stereo socket. Check that the AXE027 USB Download Cable is inserted into the correct USB port. Check that the PICAXE Programming Editor software is set to the appropriate COM port. Move the power switch to "off". Disconnect the AXE027 USB Download Cable from the stereo socket on the PCB. Position the jumper to the "run" position. SECTION 7: FUNCTIONAL TEST NOTE: The functional test can only be performed after the program is loaded into the PICAXE. Move the power switch to "on". Both motors should move in the same direction. To change the direction of a motor, swap its wires. Press one of the micro-switches. The motors should rotate backwards, turn in opposite directions and continue in the backwards direction. Press the other microswitch. The motors should rotate forwards, turn in opposite directions and continue in the forward direction. Do not press the micro-switches for a period of time (about 15 seconds). After this time, the motors go through a change of direction sequence. Move the power switch to "off". While pressing one of the micro-switches, move the power switch to "on". The motors should move backwards and forwards and then stop. Repeat for the other micro-switch. (This mode was developed to stop the motors turning before downloading a program.) Move the power switch to "off". Move the power switch to "on". Place BEETLE on the floor and observe it bumping into objects and altering its course. NOTE: The L293D will become warm with continuous use. 9

10 SECTION 8: FURTHER DEVELOPMENT We encourage you to change the program after you have determined that our program works with your BEETLE. You may use the following investigations to customise the way in which your BEETLE interacts with its environment. NOTE: At this stage nothing will appear to be working. NOTE: For programming language details, from the PICAXE "Programming Editor" help menu, open "PICAXE Manual 2 - BASIC Commands". A flowchart is a graphical representation of the program. When the program encounters an "end" statement, the program will stop until the power is cycled (turned off, then turned on). What condition needs to be filled for the program to end? A number of parameters are setup when the program starts running. One at a time, change the values of "wlng" (wait long), "wstp" (wait stop), "wbrf" (wait brief) and "await" (wait timer) in the following program lines. symbol wlng = 2000 'wait long = 2 seconds symbol wstp = 500 'wait stop = 0.5 seconds symbol wbrf = 100 'wait brief = 0.1 seconds let await = '15 second timer if switch not pressed As a starting point, double and then halve each parameter. (For example, change the value of "wlng" from 5000 to 10000). What effect does each of these parameters have? When moving forwards the following pair of lookup tables after label "skip_forward:" controls what happens after BEETLE bumps into an object. lookup aloop,(mstp,mrev,mstp,mlft,mstp),apins lookup aloop,(wstp,wlng,wstp,wlng,wstp),atime When moving backwards, the following pair of lookup tables after label "skip_reverse:" controls what happens when BEETLE bumps into an object. lookup aloop,(mstp,mfwd,mstp,mlft,mstp),apins lookup aloop,(wstp,wlng,wstp,wlng,wstp),atime The top line of each pair of lookup tables specifies motor directions and the bottom line specifies the time interval. Available parameters are listed in the "symbols" section of the program. If adding/deleting the number of data entries, in the following program line change the value after "to" by the same amount. for aloop = 0 to 4 The loop variable "aloop" controls which values will be loaded into "apins" and "atime". When "aloop" = 0, the first data entry is loaded; when "aloop" = 1, the second data entry is loaded; when "aloop" = 2, the third data entry is loaded; and so on. Investigate creating new sequences of actions by changing data in the lookup tables. Why should there be a pause before changing the leg direction? 10

11 SECTION 9: THEORY 9.1 CIRCUIT AND PROGRAM OVERVIEW NOTE: PICAXE documentation refers to "Input Pins" and "Output Pins", which are not the same as the physical pins on a device. To avoid confusion, in this document "leg" means a physical pin of an integrated circuit and "pin" means a logical input or output. A program can be downloaded into the PICAXE-08M2 memory to control the motors by input from switches and an internal timer. The program can be customised as desired. Block Diagram Pin0 on the PICAXE-08M2 is shared between the download circuit and one of the motor outputs. To download a program, move the jumper to the "program" position. This connects pin0 to the stereo socket. Using the download cable, connect the stereo socket to a serial port on the PC and download the program. When the program has downloaded, move the jumper to the "run" position. The PICAXE-08M2 then executes the commands in the program. When our program starts running, both motors are set to run in the forward direction. The main program loops continually to check the status of both switches on pin3 and an internal timer. When either switch has been pressed or the timer has expired, the PICAXE-08M2 outputs a timed sequence of high/low voltages on pin0, pin1, pin2 and pin4. Responding to the high/low voltage sequence on its inputs, the L293D opens/closes the electronic switches in its H- bridge circuits. Each H-bridge circuit (consisting of two "driver" blocks) controls the direction of one motor. Consequently, the motors turn backwards, forwards and stop as commanded by the PICAXE. Circuit Diagram 9.2 ABOUT PICAXE MICROCONTROLLERS The PICAXE* is a type of IC (Integrated Circuit) called a microcontroller - another name for a single chip computer. The PICAXE has similar features to a PC: CPU (central processing unit), RAM (random access memory), ROM (read only memory), 11

12 I/O (input/output) lines, timers and A/D (analogue to digital) converters. * PICAXE is a trademark of Revolution Education Ltd. The Flash memory (EEPROM - Electrically Erasable Programmable Read Only Memory) in a PICAXE allows it to be reprogrammed many times (typically 100,000). This means that you can develop a program and constantly check the effects of changes. A PICAXE program is created using an easy to learn version of the BASIC programming language (our preferred method) or using flowcharting software. NOTE: The PICAXE is supplied containing 'bootstrap' code that enables you to download your program using the serial cable. Do not substitute the PICAXE with a blank PIC microcontroller. 9.3 PICAXE-08M2 (IC1) When the program runs, it reads the status of the two micro-switches and controls the direction of the two motors. In this case, the PICAXE behaves as a simple neural network. PICAXE Leg 1 is connected to the positive terminal (+6V) of the power supply (batteries). PICAXE Leg 2 (serial data in) is used only when transferring a program from a serial port on your PC (COM1: to COM4:) to the PICAXE. The 22k Ohm (R1) and 10k Ohm (R2) resistors must be present for reliable operation. Do not substitute other resistor values. PICAXE Leg 3 (pin4 in the program) is connected to one of the inputs to the motor driver IC to control motor M2. PICAXE Leg 4 (pin3 in the program) is connected to the micro-switches (SW2 and SW3). Leg 4 is normally tied to ground through the micro-switches, which are wired in series. When either of the micro-switches is opened, positive battery voltage appears on Leg 4 through resistor R4. PICAXE Leg 5 (pin2 in the program) is connected to one of the inputs to the motor driver IC to control motor M2. PICAXE Leg 6 (pin1 in the program) is connected to one of the inputs to the motor driver IC to control motor M1. PICAXE Leg 7 has two functions selected by the jumper on the header strip. In the "program" position, the program can be downloaded into the PICAXE. In the "run" position, Leg 7 (pin0 in the program) is connected to one of the inputs to the motor driver IC to control motor M1. PICAXE Leg 8 is connected to the negative terminal (0V) of the power supply (batteries). 9.4 MOTOR DRIVER L293D (IC2) The L293D motor driver (IC2) contains two H-bridge circuits. Each of the "driver" blocks contains transistors that work as electronic switches. H-Bridge Circuit Concept 12 Changing the voltage applied to the input pins changes the direction of current flow through the motor. Q1 low, Q2 low - motor stop Q1 high, Q2 low - motor forward Q1 low, Q2 high - motor reverse Q1 high, Q2 high - motor stop

13 9.5 CAPACITORS Typical H-Bridge Circuit The motor driver IC is simpler to use and fault-find than an equivalent circuit built using individual transistors and resistors. To view H-Bridge circuits constructed from transistors, see the "Wanderer" teaching unit on the Scorpio Technology website. Capacitor C1 (100uF) smooths battery power caused by motor switching. Capacitors C2 and C3 (0.1uF) smooth the power supply close to the ICs. Capacitors C4 and C5 (0.1uF) reduce electrical motor noise that reaches the PICAXE. Capacitor C6 reduces switch bounce from the micro-switches connected to leg POWER A red LED, D1, in series with a 220Ohm resistor is used to indicate the presence of power on the PCB assembly. The LED intensity may change during operation. Power switch SW1 is used to control power to the circuit. 13

14 'Beetle '(C)2007, 2012 PVA Tecwrite - Peter Aleksejevs THE PROGRAM 'PICAXE-08, PICAXE-08M and PICAXE-08M2 PIN SETTINGS '0 output = Left motor connection '1 output = Left motor connection '2 output = Right motor connection '3 input = Front and rear switch (1 = either switch pressed) '4 output = Right motor connection 'Symbols symbol m_fwd = % 'motor forward symbol m_lft = % 'motor left symbol m_rev = % 'motor reverse symbol m_rgt = % 'motor right symbol m_stp = % 'motor stop symbol w_lng = 5000 'wait long - for change of direction symbol w_stp = 500 'wait stop symbol w_brf = 100 'wait brief symbol a_loop = b0 symbol a_pins = b1 symbol a_time = w1 symbol countr = w2 'changes direction if switch has not been pressed for a while symbol a_wait = w3 'Initial setup let dirs = % if pin3 = 1 then terminate 'Switch pressed when power turned on. let pins = m_fwd let a_wait = '15 second timer if switch not pressed let a_wait = a_wait / w_brf 'Convert into loop cycles main_forward: let pins = m_fwd let countr = countr + 1 pause w_brf if countr >= a_wait then skip_forward if pin3 = 0 then main_forward 'check for switch skip_forward: for a_loop = 0 to 4 lookup a_loop,(m_stp,m_rev,m_stp,m_lft,m_stp),a_pins lookup a_loop,(w_stp,w_lng,w_stp,w_lng,w_stp),a_time let pins = a_pins pause a_time next a_loop let pins = m_rev let countr = 0 main_reverse: let pins = m_rev let countr = countr + 1 pause w_brf if countr >= a_wait then skip_reverse if pin3 = 0 then main_reverse 'check for switch skip_reverse: for a_loop = 0 to 4 lookup a_loop,(m_stp,m_fwd,m_stp,m_lft,m_stp),a_pins lookup a_loop,(w_stp,w_lng,w_stp,w_lng,w_stp),a_time let pins = a_pins pause a_time next a_loop let pins = m_fwd let countr = 0 goto main_forward terminate: for a_loop = 0 to 8 lookup a_loop,(m_stp,m_fwd,m_stp,m_rev,m_stp,m_fwd,m_stp,m_rev,m_stp),a_pins lookup a_loop,(w_brf,w_brf,w_brf,w_brf,w_brf,w_brf,w_brf,w_brf,w_brf),a_time let pins = a_pins pause a_time next end PROGRAM LISTING 14